Various ablative therapies such as radio-frequency ablation, microwave ablation, and laser ablation can be used to treat benign and cancerous tumors. In theory, such methods are intended to produce physiological and structural changes to cause cell necrosis or destruction of the selected target tissue. However, in practice, there are numerous difficulties in the use of ablative procedures to treat cancerous tissue; these include: (i) locating the target tissue, (ii) identifying or biopsying the disease state of the tumorous tissue, (iii) distinguishing between diseased tissue versus healthy tissue, (iv) placing and maintaining the position of the ablation apparatus within the target tissue site, (v) monitoring the progress of ablation (including the developing ablation volume), (vi) minimizing injury to adjacent critical structures, (vii) assuring complete ablation of the tumor mass (including assurance of a sufficient healthy tissue margin), and (viii) assessing degree of the completed ablation. Current ablative therapies have not considered nor provided solutions to these problems. Thus, there is a need for treating cancerous tissue, which steps include (i) locating the target tissue, (ii) identifying or biopsying the disease state of the tumorous tissue (iii) distinguishing between diseased tissue versus healthy tissue, placing and maintaining the position of the ablation apparatus within the target tissue site, (iv) monitoring the progress of ablation including the developing ablation volume, (v) minimizing injury to adjacent critical structures, (vi) assuring complete ablation of the tumor mass including assurance of a sufficient healthy tissue margin and (vii) assessing degree of the completed ablation.
An embodiment of the invention provides an apparatus for detecting and treating tumors using localized impedance measurement. The apparatus comprises an elongated delivery device that includes a lumen and is maneuverable in tissue. An impedance sensor array is deployable from the elongated delivery device and configured to be coupled to at least one of an electromagnetic energy source or a switching device. The impedance array includes a plurality of resilient members, at least one of the plurality of resilient members being positionable in the elongated delivery device in a compacted state and deployable with curvature into tissue from the elongated delivery device in a deployed state. In the deployed state, the plurality of resilient members defines a sample volume. At least one of the plurality of resilient members includes an impedance sensor and at least a portion of the impedance array is configured to sample tissue impedance through a plurality of conductive pathways. An energy delivery device is coupled to one of the impedance array, the at least one resilient member or the elongated delivery device.
The apparatus can be configured to detect, locate and identify tumorous tissue at a selected tissue site using impedance measurements such as multi-pathway measured impedance, complex impedance and impedance vector measurements. For complex impedance real and imaginary components of the impedance signal can be used to determine more refined bioelectric parameters such as interstitial and intracellular impedance and cell membrane capacitance that provide greater sensitivity and predictive power of cell necrosis or malignancy. Also, the apparatus can be configured to utilize one or more impedance measurements to monitor a target tissue site and control the course of ablative therapy before during or after the delivery of ablative energy or other treatment to the tissue site. Accordingly the apparatus can be configured to be used independently or in conjunction with another ablative apparatus such as an RF, microwave or laser ablation apparatus. Further, the apparatus can be configured to utilize multi-path impedance measurement to monitor two or more tissue volumes including a tumor volume, a developing ablation volume and an adjacent anatomical structure. Additional embodiments of the apparatus can also be configured to utilize impedance measurements such as complex, vector or locus impedance measurements to generate an image of a target tissue site and display the image to facilitate the location and monitoring of a tumor and/or ablation volume.
In the use, the apparatus would be positioned at a selected tissue site previously imaged and found to contain a tumor or other tissue mass. The apparatus would be introduced and positioned at the tissue site using the elongated delivery device or an introducing device known in the art. The impedance array would then be deployed and used to measure impedance including complex impedance and capacitance through one or more conductive pathways. This information could be analyzed by coupled logic resources and then utilized to locate the position of and borders of the tumor volume and/or identify the tumor or tissue type. Also, the information could be processed by the logic resources or other processing means to generate an image of the tissue site including the tumor volume which could utilize the locus of impedance as a way to indicate the center of the tumor mass or otherwise visually enhance the detection and display of the tumor mass. This information could then be used to position the energy delivery device to produce the desired ablation volume. Once the energy delivery device was positioned, the impedance array could then be utilized to monitor and/or control the delivery of ablative energy or therapy to the tumor volume including monitoring the size and shape of a developing ablation volume in relation to size and location of the tumor volume. This allows the medical practitioner to not only determine the degree to which the tumor volume has been ablated, but also allows for the control of the amount of healthy tissue margin around the tumor volume one or all of which allow for the determination of a desired clinical endpoint. Further, it allows the practitioner to titrate or otherwise control the delivery of energy or other ablative therapy to control rate of growth of the ablation volume (and in turn the overall ablation time) as well as the final shape and size of the tumor volume. Multiple tissue volumes can be simultaneously monitored and compared to monitor progress of the ablation volume, assure uniform ablation or necrosis throughout the tumor or ablation volume and provide real time assurance that surrounding healthy tissues and structure were not injured. For example, tissue volume at the center, and one or more peripheries of the tumor mass could be simultaneously or near simultaneously monitored to assure uniform necrosis at all locations and hence throughout the tumor volume. Impedance measurements can be taken simultaneously or sequentially at multiple conductive pathways passing through the target volume (at convergent divergent and paths) to provide a higher confidence of uniform ablation by reducing the size of un-sampled zones within the target volume as well any directional bias of the measurements. The multiple conductive pathways can be selected electronically via a controllable switching device or manually by rotational, lateral or longitudinal movement of the impedance array within the target volume. In the former case, the user could program the conductive pathways via a coupled monitoring device and in the latter, the user could rotate, advance, retract or deflect the impedance array via the elongated delivery device or via a deployment, advancement or deflection device mechanically coupled to the impedance array or delivery device. In addition to real time impedance measurement during the ablation process, measurements can also be taken post ablation at one or more pathways, (including pathways different than those used during inter-ablative monitoring) and compared to baseline measurements or an impedance database to provide a further indication of a complete ablation and/or clinical endpoint. Endpoints can also be determined based on ratios of intracellular to interstitial impedance as well as a characteristic shape of the impedance or complex impedance curve including determinations of thresholds, slopes or inflection points.
Various aspects of the invention can also be directed to display impedance measurements in a variety of manners that are both user-friendly and easily discernible by the user/medical practitioner. In an embodiment, the loci of impedance of a sample volume or an impedance vector of the sample volume can be displayed as icons to facilitate tumor identification and positioning of an energy delivery or ablative device within the tumor mass. In related embodiments logic resource of the apparatus could be configured to use impedance vector measurements to determine the radial direction of the tumor from the impedance array or energy delivery device and display this information in the form of a directional or pointing icon.